1. Field of the Invention
The present invention relates to an uninterruptible power supply system; in particular, to a full-bridge uninterruptible power supply system.
2. Description of Related Art
The conventional uninterruptible power supply (UPS) system is for continuously providing electric power to the load, and the output neutral terminals of some UPS systems may be under floating status corresponding to the input neutral terminal of the main electricity. Thus, there is a between the output neutral terminal and the output ground terminal. The floating potential according to the requirements of some specific equipment, let the voltage level between the output neutral terminal and the output ground terminal be operated within a specific voltage range, such as operation range within 8 to 10 Vac, or to operation range within 1 to 2 Vac based on being not larger than the voltage level between the input neutral terminal and the input ground terminal. Therefore, some UPS systems may generate potential unbalance, or cannot safely provide electric power to the load.
In addition, some UPS systems use isolated transformers for achieving the specific requirements of the aforementioned equipment. However, if the isolated transformers are installed, the costs and occupying spaces of the UPS system may be increased, and the total power supply conversion efficiency of the UPS system may be reduced.